1. Field of the Invention
The present invention relates to polyaspartate mixtures prepared from a mixture of polyoxypropylene polyamines and low molecular weight polyether polyamines and to their use for the production of polyureas with good hardness and flexibility.
2. Description of the Prior Art
Two-component coating compositions containing a polyisocyanate component and a polyaspartate component are known and disclosed in U.S. Pat. Nos. 5,126,170, 5,236,741, 5,489,704 and 5,516,873. The polyaspartates may be used as the only isocyanate-reactive component or they may be blended with polyols, polyamines or blocked polyamines, such as ketimines, aldimines or oxazolidines. The compositions are suitable for the preparation of high quality coatings that are abrasion resistant, solvent resistant and weather resistant.
One of the deficiencies of these polyaspartates is that when reacted with polyisocyanates they do not form coatings with a good combination of hardness and flexibility, which can be seen from the low hardnesses and elongations of the resulting coatings. One method for improving the flexibility is to prepare the polyaspartates from high molecular weight polyether polyamines, such as Jeffamine D-2000 (available from Huntsman). However, as disclosed in WO 01/07504, the reaction of equimolar amounts of this polyether polyamine with diethyl maleate to form the polyaspartate is only 78% complete after 73 days, and it takes more than 2 years for the reaction to be 100% complete.
Based on these teachings it would be expected that the preparation of a polyaspartate from a mixture of polyether polyamines would require an unacceptably long reaction time to achieve a complete or a substantially complete reaction.
Other alternatives for reducing the reaction time are also not feasible. For example, if a large excess of the ester of maleic or fumaric acid is used to reduce the reaction time, then it is necessary to remove the unreacted excess when the reaction is completed, which is a time-consuming, expensive procedure. It is also not feasible to prepare large quantities, of the polyaspartates resins in advance because it is extremely difficult to predict customers"" needs for the products and because of expensive storage and inventory costs.
Accordingly, it is an object of the present invention to provide polyasparate resins that can be reacted with polyisocyanates to obtain coatings with improved hardness and flexibility. It is an additional object of the present invention to provide polyaspartate resins that can be prepared with a short reaction time.
Surprisingly, these objects may be achieved with the polyaspartate resins according to the present invention which are prepared from a mixture of polyoxypropylene polyamines and low molecular weight polyether amines. When reacted with polyisocyanates the resulting coatings possess a good combination of hardness and flexibility. In addition, the polyaspartate resins can be prepared with a relatively short reaction time, which is surprising in view of the prior art which teaches that excessively long reaction times are required to prepare polyaspartates from polyether polyamines.
The present invention relates to polyaspartate mixtures containing
a) 5 to 50 equiv. %, based on the total equivalents of aspartate groups, of a polyoxypropylene polyaspartate corresponding to the formula 
xe2x80x83wherein
X1 represents the residue obtained by removing the amino groups from a polyoxypropylene polyamine having a functionality of n,
R1 and R2 are identical or different and represent organic groups which are inert to isocyanate groups at a temperature of 100xc2x0 C. or less,
R3 and R4 are identical or different and represent hydrogen or organic groups which are inert towards isocyanate groups at a temperature of 100xc2x0 C. or less and
n is 2 to 4, and
b) 50 to 95 equiv. %, based on the total equivalents of aspartate groups, of a polyether polyaspartate corresponding to the formula 
xe2x80x83wherein
X2 represents the residue obtained by removing the amino groups from a polyether polyamine having a functionality of n and a number average molecular weight of less than 5000, wherein the amino groups are attached to primary carbon atoms and the ether groups are separated by at least two carbon atoms.
The present invention also relates to a process for preparing these polyaspartate mixtures by
a) reacting one equivalent of unsaturated groups from maleic or fumaric acid esters corresponding to the formula
R1OOCxe2x80x94CR3xe2x95x90CR4xe2x80x94COOR2xe2x80x83xe2x80x83(III)
with 5 to 50 equiv. % of polyoxypropylene polyamines corresponding to the formula
X1xe2x80x94(xe2x80x94NH2)nxe2x80x83xe2x80x83(IV)
to form a reaction mixture containing polyoxypropylene polyaspartates a) and excess maleic or fumaric acid esters (III) and
b) reacting the excess maleic or fumaric esters formula (III) with a substantially equivalent amount of a polyether polyamine corresponding to the formula
X2xe2x80x94(xe2x80x94NH2)nxe2x80x83xe2x80x83(V)
to form a mixture of polyoxypropylene polyaspartates a) and polyether polyaspartates b).
The present invention additionally relates to polyureas prepared by reacting the polyaspartate mixtures and optionally other isocyanate-reactive compounds with polyisocyanates.